package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import org.apache.lucene.util.BitVector;
import org.apache.lucene.store.IndexInput;

class SegmentTermDocs implements TermDocs {
	protected SegmentReader parent;
	protected IndexInput freqStream;
	protected int count;
	protected int df;
	protected BitVector deletedDocs;
	int doc = 0;
	int freq;

	private int skipInterval;
	private int maxSkipLevels;
	private DefaultSkipListReader skipListReader;

	private long freqBasePointer;
	private long proxBasePointer;

	private long skipPointer;
	private boolean haveSkipped;

	protected boolean currentFieldStoresPayloads;

	protected SegmentTermDocs(SegmentReader parent) {
		this.parent = parent;
		this.freqStream = (IndexInput) parent.freqStream.clone();
		this.deletedDocs = parent.deletedDocs;
		this.skipInterval = parent.tis.getSkipInterval();
		this.maxSkipLevels = parent.tis.getMaxSkipLevels();
	}

	public void seek(Term term) throws IOException {
		TermInfo ti = parent.tis.get(term);
		seek(ti, term);
	}

	public void seek(TermEnum termEnum) throws IOException {
		TermInfo ti;
		Term term;

		// use comparison of fieldinfos to verify that termEnum belongs to the
		// same segment as this SegmentTermDocs
		if (termEnum instanceof SegmentTermEnum
				&& ((SegmentTermEnum) termEnum).fieldInfos == parent.fieldInfos) { // optimized
																					// case
			SegmentTermEnum segmentTermEnum = ((SegmentTermEnum) termEnum);
			term = segmentTermEnum.term();
			ti = segmentTermEnum.termInfo();
		} else { // punt case
			term = termEnum.term();
			ti = parent.tis.get(term);
		}

		seek(ti, term);
	}

	void seek(TermInfo ti, Term term) throws IOException {
		count = 0;
		FieldInfo fi = parent.fieldInfos.fieldInfo(term.field);
		currentFieldStoresPayloads = (fi != null) ? fi.storePayloads : false;
		if (ti == null) {
			df = 0;
		} else {
			df = ti.docFreq;
			doc = 0;
			freqBasePointer = ti.freqPointer;
			proxBasePointer = ti.proxPointer;
			skipPointer = freqBasePointer + ti.skipOffset;
			freqStream.seek(freqBasePointer);
			haveSkipped = false;
		}
	}

	public void close() throws IOException {
		freqStream.close();
		if (skipListReader != null)
			skipListReader.close();
	}

	public final int doc() {
		return doc;
	}

	public final int freq() {
		return freq;
	}

	protected void skippingDoc() throws IOException {
	}

	public boolean next() throws IOException {
		while (true) {
			if (count == df)
				return false;

			int docCode = freqStream.readVInt();
			doc += docCode >>> 1; // shift off low bit
			if ((docCode & 1) != 0) // if low bit is set
				freq = 1; // freq is one
			else
				freq = freqStream.readVInt(); // else read freq

			count++;

			if (deletedDocs == null || !deletedDocs.get(doc))
				break;
			skippingDoc();
		}
		return true;
	}

	/** Optimized implementation. */
	public int read(final int[] docs, final int[] freqs) throws IOException {
		final int length = docs.length;
		int i = 0;
		while (i < length && count < df) {

			// manually inlined call to next() for speed
			final int docCode = freqStream.readVInt();
			doc += docCode >>> 1; // shift off low bit
			if ((docCode & 1) != 0) // if low bit is set
				freq = 1; // freq is one
			else
				freq = freqStream.readVInt(); // else read freq
			count++;

			if (deletedDocs == null || !deletedDocs.get(doc)) {
				docs[i] = doc;
				freqs[i] = freq;
				++i;
			}
		}
		return i;
	}

	/** Overridden by SegmentTermPositions to skip in prox stream. */
	protected void skipProx(long proxPointer, int payloadLength)
			throws IOException {
	}

	/** Optimized implementation. */
	public boolean skipTo(int target) throws IOException {
		if (df >= skipInterval) { // optimized case
			if (skipListReader == null)
				skipListReader = new DefaultSkipListReader(
						(IndexInput) freqStream.clone(), maxSkipLevels,
						skipInterval); // lazily clone

			if (!haveSkipped) { // lazily initialize skip stream
				skipListReader.init(skipPointer, freqBasePointer,
						proxBasePointer, df, currentFieldStoresPayloads);
				haveSkipped = true;
			}

			int newCount = skipListReader.skipTo(target);
			if (newCount > count) {
				freqStream.seek(skipListReader.getFreqPointer());
				skipProx(skipListReader.getProxPointer(), skipListReader
						.getPayloadLength());

				doc = skipListReader.getDoc();
				count = newCount;
			}
		}

		// done skipping, now just scan
		do {
			if (!next())
				return false;
		} while (target > doc);
		return true;
	}
}
